TbPc2 molecule quantum-bit device. Electrons (red) from the electrodes jump onto the molecule reading out the electronic spin (orange) and the nuclear spin (green). Graphics: C. Grupe, KIT |
Quantum
computers promise to reach computation speeds far beyond that of
today’s computers. As they would use quantum effects, however, they
would also be susceptible to external interferences. Information flow
into and out of the system is a critical point. Researchers from KIT
with partners from Grenoble and Strasbourg have now read out the quantum
state of an atom directly by using electrodes. In the Nature journal,
it is reported about the stable interface between classical and quantum
world
“Normally,
every contact with the outer world changes information in a quantum
mechanical system in a completely uncontrolled manner,” explains
Professor Mario Ruben from Karlsruhe Institute of Technology. “We
therefore have to keep the quantum state stable and shielded. On the
other hand, information has to be read out in a controlled manner for
further use.”
Magnetic
molecule complexes may be a solution of this dilemma. In their center, a
metal atom with a pronounced magnetic moment, a spin, is located. It is
surrounded by organic molecules that shield the atom. “When
synthesizing this protective enclosure, we can exactly define how much
the metal atom sees of the outer world,” explains Ruben the trick of his
research project.
The
study presented is based on the metal atom terbium that was provided
with an enclosure of about 100 carbon, nitrogen, and water atoms and
then placed in the center of nanometer-sized, electric gold contacts.
Due to the properties of the molecule, the electrodes had an effect
similar to the three channels of a transistor. Electric voltage of the
middle gate electrode influenced the current through the other two
electrodes. In this way, the working point was set. Then, the molecule
was exposed to various changing magnetic fields and the jump of the spin
was reflected by the amplitude of the current curve. “By measuring
current flow, we found that the nuclear spin of the metal atom is stable
for up to 20 seconds,” says Ruben. “For quantum mechanical processes,
this is a very long time.”
Ruben
is sure that “the results will be of particular importance to
spintronics and quantum computing.” Spintronics uses the magnetic spin
of single particles for information processing. The word describes the
symbiosis of spin and electronics. Quantum computers use quantum
mechanical effects, such as the entanglement and super-position of
spins, for the parallel execution of algorithms at high speed.
Electronic read-out of a single nuclear spin using a molecular spin-transistor
